68    LANGUAGE  AND  MENTAL  DEVELOPMENT  OF  CHILDREN
infant speech would care to be so positive in this field as Btihler
or Valentine. Miss McCarthy^1 says that she found children able
to use all the most complex of sentence forms occurring in adult
conversation by the age of four and a half; but the most complex
sentences in her published records would appear to be two sen-
tences used by a child of four and a half (whose parents belonged
to one of the higher occupational groups): these sentences were
. Do you know what we got? and I know what that book's about. These
may have or may not have been learned as formulas. Until the
form itself can be varied to match a fresh situation we have no
right to say that it is a free expression. Unless we distinguish
between merely reproductive or imitative forms which have been
learned by rote as formulas and genuine free expressions (e.g.,
complex sentences with subordinate clauses of, say, condition or
concession) which reflect an ability to express a set of ideas or
events, we are missing an important point, and the failure to
note this distinction vitiates the data of the authorities quoted.
A scrutiny of the records of children's talk in Mrs Isaacs's book
is more illuminating. Her pupils were children of exceptional
ability (average I,Q\ 132) from exceptional Cambridge homes.
They were probably two or three years above average in con-
versational ability. If we take their mental age as a criterion we
may say that complex sentences with temporal clauses (introduced
by when),, noun clauses (e.g., I don't know how he does it, I thought
you would, Do you sec where it is?}_: and causal clauses (introduced
by because) were being used at the mental age of six and a half,
and that complex sentences with conditional clauses (introduced
by if), as well as adjectival clauses (e.g., Look at the part thafs in
the water', I like some one who gives you presents] came a year later.
Other kinds of clause were too infrequent to be worth mentioning.
Buhler stated that the order in which the subordinate clauses
of complex sentences appeared was as follows: first, temporal
and relative clauses and noun clauses in indirect questions, and
then causal, conditional, and final clauses. It will be seen that
' this corresponds closely with our list as compiled from Mrs
Isaacs's book with the exception that final clauses were not con-
spicuous in the talk of the Cambridge children.
7. the beginnings of free conversation
The extent of a child's power over language as an instrument
of communication will naturally be looked for in his conversa-
* D. A. McCarthy, The Language Development of the Pre-school Child (University of
Minneapolis Press, 1935).